Emit a warning when an older version of importlib_metadata is detecte…

…d to give users better guidance when this condition is present. Ref #3452.

setuptools/_importlib.py

@@ -6,7 +6,7 @@ def disable_importlib_metadata_finder(metadata):
     Ensure importlib_metadata doesn't provide older, incompatible
     Distributions.
 
-    Workaround for #3102 and #3452.
+    Workaround for #3102.
     """
     try:
         import importlib_metadata
@@ -34,13 +34,38 @@ def disable_importlib_metadata_finder(metadata):
         sys.meta_path.remove(item)
 
 
+def check_old_importlib_metadata(metadata):
+    """
+    Warn the user if an old importlib_metadata is present and might
+    cause problems.
+
+    Workaround for #3452. Remove this check after 2022-12-31.
+    """
+    try:
+        version = metadata.version('importlib_metadata')
+        parsed = tuple(map(int, version.split('.')))
+    except Exception:
+        return
+
+    if parsed > (4, 3):
+        return
+
+    msg = (
+        "`importlib_metadata` version is incompatible with the stdlib "
+        "importlib.metadata and may cause problems if plugins import "
+        "importlib_metadata. See pypa/setuptools#3452 for details. "
+        "Consider updating to importlib_metadata 4.3 or later."
+    )
+    import warnings
+    warnings.warn(msg)
+
+
 if sys.version_info < (3, 10):
     from setuptools.extern import importlib_metadata as metadata
+    disable_importlib_metadata_finder(metadata)
 else:
     import importlib.metadata as metadata  # noqa: F401
-
-
-disable_importlib_metadata_finder(metadata)
+    check_old_importlib_metadata(metadata)
 
 
 if sys.version_info < (3, 9):